1. Field of the Invention
The present invention relates to pipeline inspection tools, also known as pipeline pigs, and particularly to sensor finger modules for such pipeline pigs for inspecting the condition of pipelines to determine metal loss, cracking or pipeline distortion.
2. Summary of the Prior Art
It is known to inspect the inside of a pipeline using a pipeline pig which may comprise one or more interconnected vehicles which pass down the pipe. Pipeline inspection vehicles typically comprise a main central body to which sensors or other components are mounted. The vehicles may be equipped with cleaning tools for removing debris and contamination from the wall of the pipeline, and sensors for determining the pipeline integrity.
The pig may be towed along the pipeline, or be fitted with pressure plates which enable propulsion by a difference in pressure across the pressure plate.
Knowledge of pipeline defects is critical in preventing future pipeline failure. Defects of particular importance include cracks, regions of metal loss (due to corrosion for example), and distortions such as dents.
Metal loss and cracking are typically identified using sensors such as magnetic flux sensors and/or ultrasound sensors.
Magnetic flux sensors are particularly effective in determining regions of metal loss in the pipeline wall. Such sensors are used for example in a high resolution inspection sensor ring manufactured by the applicants of the present invention. A plurality of such sensors usually are mounted in mounted on a sensor block which is a sensor finger for pipeline inspection. There will be a plurality of such fingers, usually arranged circumferentially around the pig. Individual sensor fingers are resiliently biased against the pipeline wall using beryllium copper leaf springs so as to provide compliance over portions of the inner wall of varying diameter.
Distortions, on the other hand, are identified in the prior art using a separate tool. Typically, either a ‘gauge plate’ or a single/multi channel calliper tool are used.
A ‘gauge plate’ is a plate having a diameter typically ˜10% less than that of the pipeline bore. The gauge plate may be mounted on a pipeline inspection or cleaning tool and run along the pipeline. Any dents in the pipeline that reduce the bore radius by greater than 10% register a positive indication by the gauge plate. Unfortunately the technique suffers the problem of false indications when the tool passes round pipeline bends, valves, fittings etc. Such indications can confuse the outcome of the run. Further, there is no knowledge of the location along or around the pipeline of dents greater than 10% of radius, and no knowledge at all of dents less than 10% of radius.
An improvement on the gauge plate technique is the calliper tool. This tool has a plurality of circumferentially spaced callipers. The callipers are individually sprung and biased to engage the inner wall of the pipeline.
The single-channel calliper tool is connected to a single recording channel which records indentations in the pipeline and can determine the maximum bore reduction, indentation and ovality of the pipeline. The calliper tool can also give an indication of the location of these features along the length of the pipeline.
Alternatively, a multichannel calliper tool can be employed, having a number of independently recorded calliper channels. They may be deployed either as separate calliper tools or as separate modules on an inspection tool. They are capable of detecting narrower indentations than the single channel callipers and can report azimuth and bend angles. They are of particular use where repairs to select regions of a pipeline wall (such as the top half of the pipe) are to be performed.
The applicants have performed extensive investigations of pipeline defects and pipeline integrity and discovered that the spatially coincident combination of cracks or metal loss defects together with distortion of the pipeline is a much more dangerous combination of defects than either type of defect alone.
However, in order to determine whether metal loss defects (typically detected by a magnetic flux sensor mounted on a sensor finger) are collocated with distortions (detected for example by a calliper tool), both inspection records must be aligned in terms of distance, girth weld number and orientation to an accuracy of a few centimeters. Inaccuracies in the relatively low-tech calliper tool data leads to time-consuming error correction.
Efficiency of inspection is further reduced, since the maximum speeds of operation of calliper tools are not as high as metal loss inspection tools (designed for high speed gas pipelines).
Therefore, at its most general, the present invention proposes that the resilient biasing of a sensor finger is monitored by at least one suitable biasing sensor which detects movement of the biasing means, and hence the finger, thereby to determine the movement of the inspection sensor and hence detect distortions simultaneously with the sensing of pipe defects.
Thus, the present invention may provide an inspection sensor module for a in-line pipe inspection tool, comprising a support for mounting the module on the tool, a finger pivotally connected to the support, at least one inspection sensor at the end of the finger remote from the support, means for resiliently biasing the finger such as to tend to move the at least one inspection sensor away from the support and at least one biasing sensor for detecting movement of the resilient biasing means corresponding to movement of the at least one inspection sensor towards or away from the support.
Thus, the present invention may be embodied in the known arrangements for supporting inspection sensors, but further modified by the provision of the biasing sensor or sensors.
The support may be a platform mountable on the in-line pipe inspection tool, or may be a wall of that tool. Normally, a plurality of inspection sensor modules will be provided circumferentially around the tool, so that the movement of each inspection sensor towards or away from the support is a radial movement in the pipe.
Thus, as the tool moves along the pipe, the or each finger is biased so that the corresponding sensor(s) abuts against the inner surface of the pipe. In that position, the sensor(s) can monitor the pipe to detect defects therein. However, if a deformation in the pipe wall in encountered, the sensor(s) will move radially to conform to the pipe wall, thus moving the finger against the resilience of its biasing means. The biasing sensor will then detect that movement. Thus, simultaneous measurement of the magnetic characteristics of the pipe and the presence of deformations can be determined.
As in the known inspection sensor arrangements, a plurality of inspection sensors may be mounted in a common block, and that block mounted on the finger. The block may be pivotally attached to the finger, to enable the radially outer surface of the block to be maintained parallel to the pipe wall, and suitable biasing provided to achieve this.
Preferably, the resilient biasing means is one or more leaf springs. Thus, a first leaf spring may bear against the finger to bias the finger, and a second leaf spring may be provided bearing against the sensor block to bias that sensor block against the pipe wall. In such an arrangement, the at least one inspection sensor is preferably mounted on the first leaf spring.
In such an arrangement, it is desirable that the at least one inspection sensor is not affected by expansion or contraction of the leaf spring due to temperature changes. To achieve this, it is possible to provide first and second inspection sensors on the leading and trailing edges of the leaf spring, so that both sensors will experience the same change due to temperature changes, but will experience different changes when the leaf spring is deformed.
Normally, the at least one inspection sensor will be a magnetic flux sensor, although it is possible to mount other sensors on the finger in accordance with the present invention.
The above discussion has illustrated the present invention in terms of an inspection sensor module. A second aspect of the invention may provide an in-line inspection tool having at least one, preferably a plurality, of such inspection sensor modules. Moreover, a third aspect of the present invention may provide a method of monitoring the characteristics of a pipe using such an inspection sensor module. This aspect permits simultaneous measurement of pipe characteristics and pipe deformation.
The present invention thus permits the primary inspection data, such as cracking/metal loss data to be spacially aligned with data representing deformation of the pipe. It thus provides more accurate determination of the pipe characteristics.